Flutter DropDownButton - How to display the selected value when dropdown button gets disabled?

Question

The Flutter DropdownButton shows some strange behaviour: it displays widget disabledHint instead of the selected value when it gets disabled (which must be done by setting onChanged to null).

How can I display the selected value?

Here is my sample code:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'DropdownButton disable problem',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool _enabled = true;
  int value;
  List<DropdownMenuItem<int>> items = [
    DropdownMenuItem(
      value: 11,
      child: Text('asdf'),
    ),
    DropdownMenuItem(
      value: 27,
      child: Text('qwert'),
    ),
    DropdownMenuItem(
      value: 31,
      child: Text('yxcv'),
    )
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('DropdownButton problem'),
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            Text(
              'Disabling the DropdownButton looses its selection',
            ),
            Switch(
              onChanged: (v) => setState(() {
                _enabled = v;
              }),
              value: _enabled,
            ),
            DropdownButton(
              items: items,
              onChanged: _enabled
                  ? (v) => setState(() {
                        value = v;
                      })
                  : null,
              value: value,
            )
          ],
        ),
      ),
    );
  }
}

Solution

If you have your List of items as a List of Map and generate the DropdownMenuItems from it you will have an easier time identifying what's selected and set it as the disabledHint:

class DropdownProblem extends StatefulWidget {
  @override
  _DropdownProblemState createState() => _DropdownProblemState();
}

class _DropdownProblemState extends State<DropdownProblem> {
  bool _enabled = true;
  int value;

  List<Map> _items = [
    {
      "value": 11,
      "text": 'asdf'
    },
    {
      "value": 27,
      "text": 'qwert'
    },
    {
      "value": 31,
      "text": 'yxcv'
    },
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('DropdownButton problem'),
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            Text(
              'Disabling the DropdownButton looses its selection',
            ),
            Switch(
              onChanged: (v) => setState(() {
                _enabled = v;
              }),
              value: _enabled,
            ),
            DropdownButton(
              disabledHint: value != null
                ? Text(_items.firstWhere((item) => item["value"] == value)["text"])
                : null,
              items: _items.map((item) => DropdownMenuItem(
                value: item["value"],
                child: Text(item["text"]),
              )).toList(),
              onChanged: _enabled
                ? (v) => setState(() {
                  value = v;
                })
                : null,
              value: value,
            )
          ],
        ),
      ),
    );
  }
}

Comments

[Jemolah]

Thx. It works. Although I still have a bad feeling about building code which already must exist within DropdownButton class itself since it can display the selected value. Seems that there is space for some optimization within DropdownButton class.

[J. S.]

You might be right. You can always propose changes on GitHub.